1. Field of the Invention
The present invention generally relates to a coordinate detecting apparatus, a method of detecting coordinate, and an electronic information board system
2. Description of the Related Art
In recent years, an electronic information board called an electronic copyboard or an interactive whiteboard (IWB) is being developed.
For example, this type of the electronic information board system is structured by combining a touch panel display using a flat panel such as a liquid crystal panel or a plasma panel and a coordinate detecting apparatus for detecting a coordinate where a touch occurs on a display element face of the touch panel display.
A coordinate detecting apparatus used for an electronic information board system includes, for example, a pair of light emission sensors for optically detecting a touch position are provided on upper corners of the touch panel display. A retroreflection plate for reflecting a light from the light emission sensor is provided in a peripheral portion of the touch panel display.
For example, when an end of the indicating unit such as a dedicated stylus pen, a finger, a pointing stock or the like touches a surface of a protection glass of a touch panel display, a light from a light emission sensor is interrupted at the touch position. A light passing through a position other than the touch position reflects on the retroreflection plate and is received by the light emission sensor. Thus, a coordinate of the touch position of the indicating unit where a reflected light is interrupted is detected in the coordinate detecting apparatus.
Further, in the coordinate detecting apparatus of the electronic information board system, based on a detection signal from the light emission sensor, an angle of a light interrupted at the touch position of the stylus pen (the indicating unit) is obtained and the coordinate of the touch position is calculated using the principal of triangular survey as disclosed in Japanese Patent No. 4627781.
Further, according to another method of detecting the coordinate disclosed in Japanese Patent No. 2678231, multiple light-emitting diodes and multiple light receiving elements are arranged in a peripheral portion of the touch panel display so as to face one another in an X direction or a Y direction of the touch panel display. In this method of detecting the coordinate, the coordinate can be detected using a lowered output level of a detection signal obtained by the light receiving element when a light emitted from a light emitting element is interrupted by a stylus pen or a finger at a touch position.
However, Japanese Patent No. 4627781 calculates the position of the stylus pen or the finger based on the lowered receiving light intensity of the detected light corresponding to a shaded position caused by interruption of the light by the stylus pen or the finger. In this method of detecting the coordinate, a detection light emitted by the light emission sensor travels in parallel with the surface of the protection glass of the touch panel display and is reflected by a retroreflection plate so as to be returned through a path similar to a travelling path. The reflected light is received by the light emission sensor.
As disclosed in Japanese Patent No. 2678231, in a case where multiple light emitting elements and multiple light receiving elements are arranged in the peripheral portion of the touch panel display so as to face one another and lights emitted from the light emitting elements are received by the light receiving elements, the coordinate is calculated based on the position of one light receiving element which cannot receive the light from the light emitting elements.
In Japanese Patent No. 4627781 and Japanese Patent No. 2678231, because the light is incident on a light receiving unit of a light emission sensor or a light receiving element irradiates substantially in parallel with the surface of the protection glass of the touch panel display, a component of the reflected light caused by a total reflection on the surface of an element of the touch panel display or the surface of the protection glass is incident on the light receiving unit of the light emission sensor or the light receiving element in addition to the light reaching the light emission sensor or the light receiving element.
As such, while the reflected light from the touch panel display or the surface of the protection glass is received and the stylus pen or the finger touches the surface of the protection glass, the protection glass slightly shows flexural deformation by a pressure caused by the touch. With this, a reflection angle of the totally reflected light reflected on the surface of the protection glass changes to thereby vary the light intensity of the light reaching the light receiving element.
If the light intensity varies as such, an error occurs in detecting a coordinate position because a position where the light intensity is lowered or the lowered light intensity is detected as if the dedicated stylus pen or the finger interrupts the light. Consequently, there occurs a problem that the coordinate of the touch position cannot be accurately detected.